[O-08] Poster presentations by senior high school students

[O08-P33] The dissappearance of Bdellocephala annandalei in conjunction with environmental changes in Lake Biwa

*Runo Sato¹, Sayane Sato², Michio Kumagai³ (1.Shiga Prefectural Zeze High School, 2.Kyoto Municipal Doda Arts and Crafts High School, 3.Ritsumeikan University)

Keywords:Bdellocephala annandalei, Lake Biwa, global warming

The population of Bdellocephala annandalei, an endemic species of Lake Biwa that lives on the lake bottom, is decreasing dramatically. After the full circulation of Lake Biwa was confirmed in 2021, we conducted a survey of the lake bottom using three Autonomous Underwater Vehicles (AUV) in the North Basin of Lake Biwa during five days from July 23 to February 7, 2021. The whole circulation of Lake Biwa is a natural phenomenon that occurs in a lake that maintains an ecosystem called "deep breathing of Lake Biwa" and protects the environment because plenty of oxygen contained in the water near the surface reaches the bottom of the lake. As a result of the survey, the survival of several B. annandalei was confirmed. We obtained a lot of valuable data such as the size, number of individuals, and their habitats, etc. We also found that we need to pay special attention to two parameters: the turbidity of Lake Biwa has worsened compared to the survey in July 2012; and the temperature of the lake bottom has increased by more than 1℃ over the past 10 years.
The relationship between the survival of B. annandalei and the rise in water temperature in Lake Biwa is not obvious at this point. However, since B. annandalei originated from planarians of northern lineage that lives in an environment with a water temperature of 6℃ to 8℃, it can be assumed that a sudden rise in water temperature will affect its habitat. Monitoring of lake bottoms will continue to be important in order to utilize the field data as indicators of the global environment change.